NATIONAL UNIVERSITY OF SINGAPORE
SCHOOL OF COMPUTING
SEMESTER II (1999-2000)
EXAMINATION FOR
CS3243: ARTIFICIAL INTELLIGENCE
May 2000
Time Allowed: 2 Hours
INSTRUCTIONS TO CANDIDATES
1. This examination paper consists of FIVE (5) questions and comprises SIXTEEN
(16) printed pages including the cover page.
2. Write your answers in the blank spaces in this answer book only. Write on one side
only.
3. This is an OPEN BOOK examination.
4. Please fill in your Matriculation Number below. Also write your matriculation
number on the top right hand corner of every page.
Matriculation Number:
--
--
For Examiner’s Use Only
Marks
Question 1
Question 2
Question 3
Question 4
Question 5
TOTAL:
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2
CS3243
1.(a) Write a LISP function named “choose” that randomly returns one of the sublists
within its argument list. Thus, suppose that “greetings” is a list containing a certain
number of sublists as defined below:
(setq greetings ’( (how are you)
(good morning)
(ciao)
………
(hello) ) )
Then your function “choose” may behave as follows:
> (choose greetings)
(GOOD MORNING)
> (choose greetings)
(HELLO)
You may use the system function “random” which returns a random number
between 0 and n-1 where n is its argument. Thus (random 10) will return an integer
between 0 and 9.
(6%)
3
1.(b)
CS3243
One of the rules in ELIZA is such that when it detects one of the keywords
“unhappy”, “depressed” and “upset”, it will reply “I am sorry to hear you are
key”, or “Do you think coming here will make you not to be key”, or “Tell me
why you are key”, where key is one of the above three keywords. Write a LISP
function named “rule1” that does so. If none of the keywords is detected, “rule1”
will return nil. You must use the function “choose” that you have defined in 1(a).
Assume that the input sentences have been converted to a list form. Thus your
“rule1” may behave as follows:
> (rule1 ’(I have been rather depressed lately))
(TELL ME WHY YOU ARE DEPRESSED)
> (rule1 ’(My friends and colleagues make me very upset))
(DO YOU THINK COMING HERE WILL MAKE YOU NOT TO
BE UPSET)
> (rule1 ’(That is why I am here to seek help))
NIL
(14%)
CS3243
4
2. For each of the following statements, indicate whether you agree or do not agree or
partially agree with the statement and give reason to support your answer.
(a) MYCIN is a “Weak AI problem Solver” because it makes use of very specific
domain knowledge and thus can only apply to a very limited range of problems,
i.e. diagnosis of spinal meningitis.
(4%)
(b) The following conceptual graph is illegal as the conceptual relation “swims”
represented by an ellipse should be connected to another conceptual node
represented by a box.
(4%)
fish
swims
5
CS3243
2.(c) The following diagram cannot be labeled using constraint propagation algorithm
because the object in the diagram does not meet the assumptions required by the
algorithm. If you don’t agree with the statement, then label the diagram
accordingly.
(3%)
(d) The following diagram cannot be labeled using constraint propagation algorithm
because the object in the diagram does not meet the assumptions required by the
algorithm. If you don’t agree with the statement, then label the diagram
accordingly.
(3%)
6
CS3243
2.(e) The following expression is a well formed formula because it is formed based on
the syntactic rules of propositional calculus.
(4%)
~(AB)=~(~A~B)
(f) Minimax search is a breadth-first search.
(2%)
CS3243
7
3.(a) The following minimax search tree has static evaluation function scores with
respect to the max player for all the leaf nodes, where + denotes end of the game
with the max player winning the game while - denotes end of the game with the
min player being the winner. Use minimax search to find the values for all the nonleaf nodes. Do you get the same set of values whether you search the tree from left
to right or from right to left? Identify the leaf node which the max player is
expected to reach from the root (node A). Is it likely for the max player to win the
game within 3 moves from the root including his opponent’s move?
(8%)
A
max
min
max
E
D
C
B
-
F
J
H
G
Q
5
-6
7
9
10
-3
2
12
1
+
-4
8
K
L
M
N
P
R
r
S
T
U
V
W
X
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8
3.(b) Use alpha-beta procedure in the direction from left to right to prune the search tree.
Show alpha-beta values at appropriate nodes and indicate which arcs are to be
pruned by the procedure.
(6%)
A
max
min
max
E
D
C
B
-
F
J
H
G
Q
5
-6
7
9
10
-3
2
12
1
+
-4
8
K
L
M
N
P
R
r
S
T
U
V
W
X
(c) Repeat the alpha-beta procedure but this time from right to left. Show alpha and
beta values at appropriate nodes and indicate the arcs to be pruned.
(6%)
A
max
min
max
E
D
C
B
-
F
J
H
G
Q
5
-6
7
9
10
-3
2
12
1
+
-4
8
K
L
M
N
P
R
r
S
T
U
V
W
X
CS3243
9
4. Referring to Fig 11.7 in the text book (or slide 10.19 in the note), the “NUMBER” of
a noun or a verb is either ‘singular’ or ‘plural’ or both. In fact, the “NUMBER”
should carry another piece of information, namely, ‘person’ in addition to being
‘singular’ or ‘plural’. For instance, “I” and “we” are 1st person, “you” is 2nd person,
“he”, “she”, “it”, “they” and all other nouns are 3rd person. Among them, “I”, “he”,
“she”, “it” are ‘singular’, while “we” and “they” are ‘plural’. On the other hand,
“you” may be ‘singular’ or ‘plural’. Other nouns have their own ‘singular’ and
‘plural’ forms. Also, “I”, “we”, “you”, “he”, “she”, “it” and “they” belong to a
special group of nouns. Their part-of-speech is known as “pronoun”. To represent
‘person’ together with ‘singular’ or ‘plural’, we will now use the following notations
for “NUMBER” as follows:
Number
1S
2S
3S
1P
2P
3P
Meaning
1 person singular
2nd person singular
3rd person singular
1st person plural
2nd person plural
3rd person plural
st
As a result of the above new definition for “NUMBER”, every verb will carry a
corresponding “NUMBER” to match with the noun or pronoun in a sentence, based
on the context. For instance, the word “am” which is a verb has the “NUMBER” 1S
(as in “I am”), while another verb “are” has the “NUMBER” 1P, 2S, 2P or 3P (as in
“We are”, “You are” or “Men are” etc).
Now we assume that an Augmented Transition Network (ATN) has the following
words in its dictionary entries:
I, you, we, he, she, it, they, man, men, am, is, are, run, runs
Note that the verbs “am”, “is” and “are” all have the same root form, i.e. “be”.
Moreover, the ATN has a simple set of context free grammar rules as follows:
sentence

noun_phrase
noun_phrase

pronoun
noun_phrase

noun
verb_phrase

verb
verb_phrase
10
CS3243
4.(a) Draw the transition networks for “sentence”, “noun_phrase” and “verb_phrase”,
repectively, used by the ATN based on the context free grammar given above. You
need not define the procedures used by the transition networks.
(4%)
CS3243
11
4.(b) Complete the dictionary entries for the ATN as follows:
Word
I
you
we
he
she
it
they
Definition
Part_of_Speech:
Word
man
Definition
Part_of_Speech:
Root:
Root:
Number:
Number:
Part_of_Speech:
men
Part_of_Speech:
Root:
Root:
Number:
Number:
Part_of_Speech:
am
Part_of_Speech:
Root:
Root:
Number:
Number:
Part_of_Speech:
is
Part_of_Speech:
Root:
Root:
Number:
Number:
Part_of_Speech:
are
Part_of_Speech:
Root:
Root:
Number:
Number:
Part_of_Speech:
run
Part_of_Speech:
Root:
Root:
Number:
Number:
Part_of_Speech:
runs
(9%)
Part_of_Speech:
Root:
Root:
Number:
Number:
CS3243
12
4.(c) Complete the following parse tree for the following sentence:
Men run.
Explain how the ATN ensures that the “NUMBER” of the noun phrase agrees
with the “NUMBER” of the verb phrase.
(7%)
Sentence
Noun_phrase:
Verb_phrase:
Noun_phrase
Verb_phrase
Noun:
Verb:
Number:
Number:
CS3243
13
5.
A person decides whether to eat at a restaurant based on two factors, namely, how
expensive the food is as shown on its menu and whether there is a queue waiting
outside the restaurant and if so, how long the queue is. He has drawn up a decision
table as follows:
Rule
1
2
3
4
5
6
7
8
9
Price of food on menu
expensive
expensive
expensive
reasonable
reasonable
reasonable
cheap
cheap
cheap
Queue Waiting outside
No queue
Short queue
Long queue
No queue
Short queue
Long queue
No queue
Short queue
Long queue
To eat here or not?
No
No
No
Yes
No
No
Yes
Yes
Yes
He has also computed the information content of the above decision table based on
the probabilities of his two decisions (i.e. yes or no) as follows:
I (decision table) = - P(yes) log2 P(yes) - P(no) log2 P(no)
= -
4
4
log
2 9
9
= 0.991 bits
-
5
5
log
2 9
9
14
CS3243
5.(a) Suppose that the person wants to use the property “price of food on menu” (which
we will abbreviate to “price”) as the root to construct a decision tree. Compute (i)
the expected information needed to complete the decision tree and (ii) the
information gain from the property “price”, i.e. find E(price) and gain(price). The
following mathematical formulas may be useful for your computation.
a
n b =
logn a - logn b
log
log2 1 = 0
log2 2 = 1
log2 3 = 1.585
log2 4 = 2
log2 5 = 2.322
log2 6 = 2.585
log2 7 = 2.808
log2 8 = 3
log2 9 = 3.170
(8%)
15
CS3243
5.(b) Suppose that the person wants to use the property “queue waiting outside” (which
we will abbreviate to “queue”) as the root to construct a decision tree. Compute (i)
the expected information needed to complete the decision tree and (ii) the
information gain from the property “queue”, i.e. find E(queue) and gain(queue).
The same mathematical formulas are reproduced for your use.
a
n b =
logn a - logn b
log
log2 1 = 0
log2 2 = 1
log2 3 = 1.585
log2 4 = 2
log2 5 = 2.322
log2 6 = 2.585
log2 7 = 2.808
log2 8 = 3
log2 9 = 3.170
(7%)
16
CS3243
5.(c) Which property should the person choose as the root to construct his decision tree?
Why? Draw the decision tree of his choice as follows.
(5%)
END OF PAPER